Endoscopy is a medical field which allows the acquisition of high-quality video images of internal features of a human body, without the need for invasive surgery. A basic tool of endoscopy is an endoscopic camera system, which includes a scope that is inserted into the body of a patient. Some endoscopic procedures involve the use of a flexible scope, as in the field of gastroenterology, for example. Other procedures, such as arthroscopy or laproscopy, involve the use of a rigid scope. The scope is normally coupled to a camera head that includes electronics for acquiring video image data through the scope.
The coupled scope and camera head may be held and manipulated during endoscopic surgery by a human surgical assistant or by a holding tool, such as a robotic positioning system. The scope has optical properties which allow it to introduce light into the body of the patient and to transmit light from the body cavity. An optical coupler is generally used to connect the endoscope to the camera head and to transfer the image from the endoscope to the camera head. The camera head is then coupled through a flexible transmission line to a camera control unit, which is often mounted on a mobile cart. The control unit processes video data provided by the camera head to generate images, which are displayed on a video monitor. The control unit may also be coupled to various peripheral devices, such as a printer and a videocassette recorder (VCR).
Although the coupler can have the ability to perform various functions, such as zoom or rotation of the image to change the orientation of the image on the video camera, a coupler typically has the ability to focus the image coming from the endoscope. The focusing function causes the light beams to converge. Focusing is realized when the focal point coincides with a solid-state image sensor, such as a charge coupled device (CCD), incorporated in the camera head. One way of accomplishing this is to install optical components, such as lenses or prisms, within the coupler and attach the camera and scope to the coupler, so that all the components are in optical communication with each other. By moving the optical components relative to either the camera, the scope, or both, the focal distance of the image can thereby be altered, such that focusing is realized.
Because the coupler is used in the medical operating environment, sterilization is necessary before and after each use. Steam autoclaving is a common method of sterilization and is used for many medical instruments that can withstand the necessary high temperature and pressure. The autoclave process can require the instrument to withstand, for example, 135° C. high-pressure vapor for five minutes. Instruments that will not survive the autoclave process are normally sterilized by less efficient techniques, such as immersion in sterilization liquid or gas.
Typically, optical systems are very sensitive to condensation caused by moisture, particularly the moisture in an autoclave environment. Problems that occur with prior art couplers are that moisture from autoclaving is able to penetrate the interior of the optical chamber, causing fogging (condensation) of the lenses and other optical components to occur, which inhibits the coupler's ability to transfer an image from the scope to the camera. A challenge in designing an optical coupler is to prevent moisture from autoclaving and other sources from penetrating the lens system.
One type of endoscope coupler includes a cylindrical body closed at opposite ends by transparent windows and containing a lens holder carrying one or more lenses to optically adjust an endoscopic image onto an image sensor in the camera. The coupler is threaded to accept a camera housing at one portion and an endoscope at the other portion. Focusing is commonly achieved by the user turning a focus ring of the coupler or by operating an electronic control, which translates the lens system inside the coupler. This action varies the distance between the lens and the CCD and allows the image to be focused onto the CCD plane. An illustrative coupler of this type is disclosed in U.S. Pat. No. 6,069,651 (Tsuyuki et al.), which discloses a coupler with a scope attached to one side and a camera attached to the other. As the user turns a focus ring, the lens assembly moves laterally between the camera and scope, which remain at a fixed distance from each other. In this design there is no ability to adjust the focus by altering the distance between the scope and the camera.
The aforementioned U.S. Pat. No. 6,069,651 (Tsuyuki et al.) discloses another endoscopic coupler embodiment where the distance between the scope and lenses is fixed. Turning the camera head, which is provided with threads, can alter the distance between the camera and the fixed scope and lenses. In this design, the camera head provides the ability to alter the distance between the endoscope and the camera. Because the camera head itself facilitates the movement, the camera head must be manufactured with special threads for adjustably coupling the camera head to the coupler body. Furthermore, the camera head must be specially designed to be autoclavable.